The corrosion behavior and corrosion resistance of WE43 and AZ80 immersed in NaCl and Na2SO4solutions were investigated, respectively. Two alloys were immersed in 0.6 M NaCl and Na2SO4solution to observe the corrosion morphologies. Hydrogen evolution and weight loss experiments were conducted to obtain the corrosion rates. Electrochemical tests were used to characterized detailed corrosion situation. The results show that, when immersed in Na2SO4solution, WE43 alloy shows a unique micro-galvanic corrosion behavior. On the other hand, the corrosion rate of WE43 in Na2SO4solution is much faster than that in NaCl solution, which is the direct opposite of AZ80 and most magnesium alloys. The protection of the surface film maybe the key factor to the unexpected phenomena.Keywords:magnesium alloys;rare earth elements;micro-galvanic corrosion;surface film;corrosion resistance
Magnesium is considered one of the most promising anode materials. However, it is easy to react with electrolyte to form an ionic insulating passive film, causing a common phenomenon of voltage hysteresis and the resultant deteriorated electrochemical performance for magnesium batteries . Here, the voltage hysteresis of magnesium-sulfur batteries in Mg(ClO 4 ) 2 electrolyte is confirmed to be a consequence of magnesium passivation through three-electrode test and electrochemical impedance spectroscopy (EIS) measurements. The continuous competition relation between the formation and destruction of the passive film during magnesium stripping is discovered. The destruction process is controlled by the current density on magnesium anode, and the formation process is mainly affected by the concentration of anions causing passivation. Bromide ions as electrolyte additive can protect the magnesium surface from ClO 4 − anions and regulate the composition and thickness of the surface film, and the passivation of magnesium and the voltage hysteresis can be suppressed obviously. This work provides an important reference for further regulation of passivation behavior of magnesium anode.
Lihua Jiang,Chen Liang,Huang Li,Qingsong Wang,Jinhua Sun
Flammable carbonate-based electrolyte greatly limits the safe application of lithium ion batteries with poor high-temperature performance. The key to developing safer electrolytes is to achieve a completely nonflammable fire safety property and meanwhile ensure a good electrochemical performance. In this study, a nonflammable electrolyte consisting of 1.0 M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) in triethyl phosphate (TEP) with a modified surface-film-forming additive is proposed. Against the disadvantages of concentrated electrolytes, surface-film-forming additives including vinylene carbonate (VC) and fluoroethylene carbonate (FEC) help to construct a low-concentration electrolyte with higher ionic conductivity and lower viscosity. Surface morphology and elemental analyses for the electrodes also confirm that the additive promotes the participation of lithium salt during the formation of surface film and inhibits the decomposition of TEP and the deposition of a phosphide layer. A significantly extended cycle life for cells employing several kinds of electrodes including LiNi0.8Co0.1Mn0.1O2 (NCM811), LiFePO4 (LFP), and Li4Ti5O12 (LTO) is obtained by the suggested TEP-based electrolyte. In particular, reversible cycles are realized for NCM811 up to 50 times even under 100 °C. It is believed that this nonflammable electrolyte with high-temperature endurance and good electrochemical performance is a possible candidate for the next generation of lithium ion batteries.
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